1. Field of the Invention
The present invention relates to a liquid crystal composition, a liquid crystal display device and a liquid crystal displaying method making use of this liquid crystal display device.
2. Description of the Background Art
A liquid crystal display device serves to display the intended image by applying an electric field to a liquid crystal layer containing a liquid crystalline compound to control the state of molecular orientation of the liquid crystalline compound in the liquid crystal layer, and those of various systems have heretofore been known.
However, the conventional liquid crystal display devices are such that the state of molecular orientation of the liquid crystalline compound is maintained in a state that the effect of the electric field is continued, whereby the displayed state is retained, while the state of molecular orientation of the liquid crystalline compound is not maintained when the effect of the electric field is ceased, whereby the displayed state is dissolved. There has thus been a demand for development of a liquid crystal display device by which the displayed state is retained even after the effect of the electric field is ceased.
The present invention has been made on the basis of the foregoing circumstances and has as its first object the provision of a liquid crystal composition by which the state of molecular orientation of a liquid crystalline compound can be stably maintained even when no electric field is effected, and moreover the state of molecular orientation of the liquid crystalline compound can be changed.
The second object of the present invention is to provide a liquid crystal display device by which a displayed state can be stably retained even after the effect of an electric field is ceased, and moreover the displayed state can be dissolved with ease.
The third object of the present invention is to provide a liquid crystal displaying method by which a displayed state can be stably retained even after the effect of an electric field is ceased, and moreover the displayed state can be dissolved with ease.
According to the present invention, there is thus provided a liquid crystal composition comprising a liquid crystalline compound and a liquid crystal orientation state-regulating agent for regulating the orientated state of the liquid crystalline compound by gelling, wherein a phase transition temperature between an isotropic liquid phase and a liquid crystal phase in the liquid crystalline compound is higher than a gelling temperature by the liquid crystal orientation state-regulating agent.
In the liquid crystal composition according to the present invention, the liquid crystal orientation state-regulating agent may preferably be one that forms fibrous aggregates oriented in the same direction as the liquid crystalline compound in a state that the liquid crystalline compound has been oriented in a direction.
The liquid crystal orientation state-regulating agent may preferably be composed of a compound having at least one group capable of forming an intermolecular hydrogen bond and at least one alkylene group in its molecule.
The liquid crystal orientation state-regulating agent may preferably be composed of a compound having a group represented by the following general formula (1): 
xe2x80x83wherein R1 means a hydrogen atom or a monovalent organic group.
In the liquid crystalline compound according to the present invention, the liquid crystal orientation state-regulating agent may preferably be contained in a proportion of 0.05 to 30.0% by weight based on the total weight of the liquid crystal orientation state-regulating agent and the liquid crystalline compound.
According to the present invention, there is also provided a liquid crystal display device comprising a liquid crystal layer formed of the liquid crystal composition described above.
According to the present invention, there is further provided a liquid crystal displaying method comprising;
cooling a liquid crystal layer formed of the liquid crystal composition described above to a temperature not higher than a phase transition temperature between an isotropic liquid phase and a liquid crystal phase in the liquid crystalline compound in a state that the liquid crystalline compound is in the isotropic liquid phase while causing an electric field to effect on the liquid crystal layer in the thickness-wise direction thereof according to a display pattern, whereby the liquid crystalline compound is transformed from the isotropic liquid phase to the liquid crystal phase; and
cooling the liquid crystal layer in the state of the liquid crystal phase, to a temperature not higher than a gelling temperature by the liquid crystal orientation state-regulating agent, whereby the liquid crystal composition is gelled.
According to the liquid crystal composition of the present invention, the liquid crystal composition is cooled to a temperature not higher than the phase transition temperature between the isotropic liquid phase and the liquid crystal phase in the liquid crystalline compound in a state heated to a temperature higher than the phase transition temperature while causing an electric field to effect on the liquid crystal composition or without causing an electric field to effect, whereby the state of molecular orientation of the liquid crystalline compound can be controlled. The liquid crystal composition is then cooled to a temperature not higher than the gelling temperature by the liquid crystal orientation state-regulating agent, whereby the fluidity of the liquid crystal composition is lost by the liquid crystal orientation state-regulating agent, and the state of molecular orientation of the liquid crystalline compound is regulated, so that the state of molecular orientation of the liquid crystalline compound can be stably retained even after the effect of the electric field is lost. The liquid crystal composition is heated again to a temperature higher than the phase transition temperature between the isotropic liquid phase and the liquid crystal phase in the liquid crystalline compound, whereby the liquid crystal composition turns into an optically isotropic liquid, so that the state of molecular orientation of the liquid crystalline compound can be changed.
According to the liquid crystal display device of the present invention, the liquid crystal layer, which has been heated to a temperature higher than the phase transition temperature between the isotropic liquid phase and the liquid crystal phase in the liquid crystalline compound, is cooled to a temperature not higher than the phase transition temperature while causing an electric field to effect on the liquid crystal layer in the thickness-wise direction thereof according to a display pattern, whereby the liquid crystalline compound is transformed from the isotropic liquid phase to the liquid crystal phase, thereby forming light-transmitting portions and light-scattering portions in the liquid crystal layer to provide the intended display pattern. The liquid crystal layer in such a state is then cooled to a temperature not higher than the gelling temperature by the liquid crystal orientation state-regulating agent, thereby gelling the liquid crystal layer so that the display pattern formed in the liquid crystal layer is being fixed.
In the state that the liquid crystal layer is at a temperature not higher than the gelling temperature by the liquid crystal orientation state-regulating agent, the state of molecular orientation of the liquid crystalline compound is regulated by molecules of the liquid crystal orientation state-regulating agent, so that the state of molecular orientation of the liquid crystalline compound remains unchanged even after the effect of the electric field is ceased. Accordingly, the light-transmitting portions and light-scattering portions in the liquid crystal layer are retained as they are, so that the displayed state is stably retained.
The liquid crystal layer is heated again to a temperature higher than the phase transition temperature between the isotropic liquid phase and the liquid crystal phase in the liquid crystalline compound, whereby the displayed state is dissolved.